U.S. television stations are set to make the long-anticipated switch to all-digital broadcasts Friday, a transition that could leave many Americans without television service.

By Saturday, all television stations in the United States will shut off their analog signals, which have been used for more than half a century.

The transition only affects free over-the-air transmissions, which means the majority of Americans, who use cable or satellite to receive television, will not be affected.

However, researchers estimate that nearly three million homes may not be ready for the switch, including the elderly, non-English speakers, and rural residents.

The government made a major effort to prepare for the switch, including offering $40 coupons to help people buy converter boxes needed to receive digital signals on older television sets.

Telecommunications companies spent $20 billion for the rights to use the old analog airwaves, which will be used to transmit new services for mobile phones, and also as a communications network for emergency responders.